Understanding how the urothelium grows and differentiates is central to understanding a number of bladder diseases. Being able to modulate these processes would allow us to improve how we repair urinary tract abnormalities in children. Preliminary evidence in our laboratory suggests that Secreted Protein Acidic and Rich in Cysteine (SPARC) plays an important role in regulating DNA synthesis and shape change of urothelial cells, which are two crucial processes involved in control of growth and differentiation of the urothelium. Other processes include a complex network of crosstalk communication between the urothelium and the mesenchyme. We propose to attack the SPARC part of this process because a) nothing is known about the biology of SPARC in the bladder and b) an understanding of how SPARC works in conjunction with these other processes will allow us to develop new and innovative methods to strengthen our translational approach to the problem of bladder and urinary tract disease. In order to achieve these goals, we have established specific aims for this period of support to better understand how SPARC functions in the context of a dynamic steady-state interrelationship that suppresses the progression of the urothelial cell cycle and mediates the attachment of urothelial cells to its underlying basement membrane. A dual role for SPARC in regulating these process is hypothesized to depend on whether SPARC is secreted or whether it remains inside the cell or nucleus. We propose that abundant levels of intracellular SPARC define the normal urothlelial phenotype - that of quiescence. During the proliferative phase, SPARC is no longer sequestered within cells, but instead is secreted into the extracellular space where it contributes to changes in cell shape that accompany the dismantling of focal adhesions, spreading, and a formation of the invasive phenotype. Information gained from this research will provide us with a basic descriptive understanding of SPARC function that we will use to design SPARC implants that will be tested clinically or in animal models by which SPARC modulates urothelial function.